It was increasingly difficult "to reach the hardest-hit places" after almost two years of continuous fighting, upheaval and civil war, she said.

The UN estimates that more than 60,000 people have been killed in the war-torn country since March 2011.

The program has been using several local organizations to distribute food inside the country, including the Syrian Arab Red Crescent. But they are struggling with a "lack of capacity" and escalating violence.

"Our main partner, the Red Cross, is overstretched and has no more capacity to expand further," Byrs said.

In response to the growing violence, the World Food Programme has pulled its staff out of its offices in Homs, Aleppo, Tartus and Qamisly, reported the BBC.

The Guardian reported that in the last few months, there has been a sharp increase in the number of attacks on its trucks carrying food aid and about 10 had been stolen or confiscated.

"In many of these incidents, WFP was able to recover the food after negotiations through third parties, but truck drivers have become more reluctant to drive on some roads or deliver food assistance to risky areas," WFP said.

Much of the country is also running out of wheat and many bakeries in the capital Aleppo are being forced to shut down.

In December, a government airstrike on a bakery in Hama province in central Syria killed and wounded more than one hundred people, reported CNN.